The present invention relates to a magnetic tape unit such as a DAT (Digital Audio Tape Recorder), specially to the construction of the rotatable drum portion thereof.
Conventionally, there has been proposed a magnetic tape unit as disclosed in the Japanese Utility Model Laid-open Publication No. 61-61611, wherein as shown in FIG. 6, the components such as a rotatable drum 2 provided with a magnetic head (not shown) that spins around a rotational shaft 1, a fixed drum 3 for supporting the rotatable drum 2, a supporting member 4 for supporting the fixed drum 3 and a motor 5 to rotate the rotatable drum 2 altogether compose a rotative head component 6, which is fixed to a base plate 8 through a screw 7 at the outer edge portion 4a of the supporting member 4.
In the magnetic tape unit of the above construction, the supporting member 4 is generally constructed from a diecast Zinc or a resin-formed material, whereas the base plate 8 is made from a metal plate mainly adopted for economical reason. The materials of the above two objects are thus different from each other in the respective coefficients of thermal expansion and also in the degrees of expansion and contraction against the temperature fluctuation therearound, whereby at least one of these materials is deformed to produce a positional error between the base plate 8 and the rotative head component 6. On the other hand, the magnetic tape (not shown) is brought into contact with the rotatable drum 2 and the fixed drum 3 through a tape guide mechanism (not shown) provided on the base plate 8, thereby a predetermined angle (hereinafter referred to as "tape inclination angle") against the rotation surface of the magnetic head is formed so as to write/read signals to/from the surface of the magnetic tape.
Accordingly, when the subtle positional error occurs between the base plate 8 and the rotative head component 6 in accordance with the temperature fluctuation, the above tape inclination angle is not possibly maintained, and the magnetic head thereby becomes unable to read the signals stored on the magnetic tape. This phenomenon is applied specially to the vehicle-mounted type magnetic tape unit which is seriously affected to its proper operation by the abrupt temperature fluctuation generated inside the vehicle.
The primary object of the present invention therefore is to eliminate the above problems contained by the conventional unit, in other words, to provide a magnetic tape unit, wherein the predetermined tape inclination angle is not affected by any temperature fluctuation therearound.